Project 2. In Vivo Kinetics of Mesenchymal Stromal Cell-Derived Exosomes and Soluble Factors. ABSTRACT Allogeneic stem cell transplantation (AlloSCT) is a potentially curative procedure for otherwise incurable cancers. However, this therapeutic approach is associated with a life-threatening immune-mediated inflammatory process known as acute graft-versus-host disease (aGVHD), which occurs in as many as 70% of transplant patients. Why some patients are tolerant to AlloSCT and others experience severe immune complications from this procedure is unknown. Ex vivo cultured mesenchymal stromal cell (MSC) infusions are an experimental cellular therapy for the treatment of aGVHD and several other inflammatory/immune diseases. When MSCs are infused into the peripheral blood, they release immunomodulatory signaling factors comprised of proteins, cytokines, chemokines, and extracellular vesicles (including exosomes). Drs. Dunavin (Leader of Project 2), McGuirk (COBRE mentor, KUMC), and Weiss (COBRE mentor, KSU), in collaboration with the Midwest Stem Cell Therapy Center at the KU Cancer Center, have developed a novel MSC preparation derived from umbilical cord Wharton?s jelly (product called MSCTC-0010, IND#17672) and have designed a phase I study for treatment of aGVHD. However, one of the central problems affecting all MSC-based therapies continues to be defining the optimal dose and duration of therapy to maximize clinical benefit for any given patient. Therefore, we propose bench-to-beside research studies to establish the temporal modifications in MSC-derived soluble factors which abrogates the inflammatory response. We will address cellular events regulated by these changes and identify molecules that can be used as surrogates for in vivo kinetics to help predict response to a dosing schedule. Our goal is to ultimately improve the efficiency and efficacy of MSC therapies in patients being treated for GVHD. Therefore, we propose to 1) Establish the temporal qualitative and quantitative changes in MSC-derived exosomes and soluble factors using a xenogeneic aGVHD mouse model; 2) validate MSCs-derived exosome- associated markers using a preclinical xenogeneic mouse model (exosomal therapy strategy); and 3) identify molecules that can be used as surrogates to predict response to dosing schedule of MSCTC-0010 in patients. Understanding the kinetics of immune modulation following MSC infusion and identifying predictive biomarkers of GVHD severity will support efforts to identify those patients most likely to benefit from MSCs as well as determine the optimal treatment course. The proposed studies will be advanced with the support of the three research COBRE cores and the ?Patient and Community Engagement? program by i) coordinating the collection of clinical trial specimens for biomarker analyses; ii) identifying and validating predictive biomarkers in clinical samples; iii) providing novel microfluidic platforms to capture and characterize MSC-derived exosomes from peripheral blood; and iv) offering engagement strategies to enhance patient-centeredness. Results from these studies will help guide how MSC-based therapies can be most effectively delivered to enhance the care of cancer patients receiving curative treatment by diminishing life-threatening side effects of stem cell transplantation.